Reproduction in Domestic Animals

Ethical Models for Studying Reproduction 9research students), and they may even benefit theanimals themselves (new cures, better managementpractices). The cost side of the equation includesimpositions made on animals for the purpose of theexperimentation and can include the pain of procedures,lack of environmental stimulation (e.g. lack of contactwith conspecifics), or food restriction. Final assessmentof the cost–benefit ratio is fairly subjective becausesuffering is not easily quantified and the benefits areusually a ‘best-guess’. However, any attempt to decreasethe cost to the animals for a given benefit will increasethe ethical value of an experiment. A good way todecrease the cost is to adopt more ‘humane’ approachesto animal experimentation. In this context, the ‘Principleof 3 Rs’ (3Rs) originally proposed by Charles Hume, thefounder of the University Federation for AnimalWelfare (UFAW) in 1954, and later defined in greatdetail in the seminal book by Russell and Burch (1959),a valuable resource. In brief, the 3 Rs’ areReplacement – substitution of insentient material forconscious animals;Reduction – get the same amount of information fromfewer animals;Refinement – decrease the imposition on the animalsused in the research.The 3Rs is widely used by animal ethics committeesaround the world to assess animal-based research,including experimentation in the field of reproductivebiology. Replacement is seen as the ultimate ethicalsolution, but that does not mean that cell culture andmathematical models should replace live animal experimentation.Many theories can ultimately only be testedin whole organisms, as is very well demonstrated inresearch for drug discovery, even if some drugs tested onanimals turn out to be dangerous to humans (Festingand Altman 2002). In fact, cell lines, such as immortalizedGnRH neurons, have been intensively used to studythe regulation of the reproductive function (Wetsel1995).Knowledge in Reproductive Physiology: A Curseor a Blessing?Regardless of the level of the investigation of thereproductive system, from cell physiology to behaviour,it is important for the researcher to be cognizant of themultiplicity of factors that influence the reproductiveprocess, as illustrated in Fig. 1. The complexity of theinputs is both a curse because perfect experimentaldesign requires the control of all of these factors, and ablessing because a deep knowledge of how these factorsinfluence experimental outcomes gives us a strong graspof the factors that we need to control in our experimentaldesign. In accounting for all factors that affectreproduction, we account for more variability and thepower and precision of our experiments is increased,improving the ethical outcomes of refinement andreduction (Howard 2002). Some factors are easier tocontrol than others, especially when large groups ofanimals are required. Importantly, many of these factorsare not independent so interactions among them (e.g.nutrition, photoperiod and genotype; Blache et al. 2006,2007) can lead to complex outcomes but, because theyPhotoperiodicsignalsPinealmelatoninGenotypeAnnualrhythmgeneratorOestrogenAromataseNegativefeedback‘Emotional reactivity’AppetitePhotoperiod-driven filterNutritionalsignalsMetabolicSensor“Pulse generator”GnRH pulsesLH, FSHSex steroidsSexual behaviourSocio-sexualsignalsOestrogenAromataseNegativefeedbackFig. 1. A schema describing the proposed relationships betweenemotional reactivity and external inputs (photoperiod, nutrition andsocial signals) and the ways that they interact with genotype andsteroid feedback in the control of hypothalamo–pituitary–testicularaxis in the male sheep. The interactions indicated with broken lines areeither hypothetical or demonstrated (see text) but the nature of thesepathways is not fully understood in ruminants. Redrawn after Blacheet al. (2007)have been extensively studied, we have excellent opportunitiesto apply the 3Rs. Below, we will illustrate thispoint by showing how controlling for genotype, nutritionand temperament can lead to more ethical animalexperimentation.Genetics and ethical experimentationDuring the last decade, there has been a dramaticincrease in the use of genetically modified animals, suchas conventional inbred lines, or lines carrying deletedgenes (knock-out), additional genes (knock-in), or overexpressedgenes (transgenic). In the UK, the number ofgenetically modified animals used in research more thanquadrupled between 1995 and 2006 and are they nowused in 34% of all procedures (Home Office 2007). Theyare considered better experimental models than theirwild-type counterparts because they exhibit less variabilityand ⁄ or they have a modification that allowsexperiments to target a specific function, gene ormolecule (Festing 1990; Festing and Altman 2002). Inreproduction, the knock-out rodent models have confirmedand informed our understanding of, for example,the role of sex steroid hormones in many of the stages ofthe reproductive process. This has been clearly demonstratedfor the oestrogen receptor in females and theandrogen receptor in males (De Gendt et al. 2004;Hewitt et al. 2005). Similarly, animals with an engineereddeficiency in FSH and LH production, or theirreceptors, or in metabolic hormone receptors, have alsocontributed to advances in our knowledge of reproductiveprocesses and how those processes interact withother functions and systems (Kumar 2005). However,these models cannot completely substitute for ‘geneticallyintact’ animals because of the plasticity,Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag